The present invention is directed to a method and apparatus for controlling the timbre of audible tones produced by an electronic musical instrument. In particular, the invention is directed to a scheme of varying the decay pattern of the composite audible tone to simulate the audible tones of a piano or other percussive instrument such as a harpsichord, clavichord, guitar, banjo and so forth, and to synthesize, polyphonically, a wide variety of popular "electronic" tones.